No signal to monitor when waking up after sleep

Bought myself a new PSU (Corsair AX750) and the problem seems to have resolved itself. Left the computer sleeping during the night and woke it up without any issues this morning. I will have to do some more testing to confirm it and will update both this answer and my question when I got the results.

Thanks a bunch to CarlF and Shinrai for their input on the matter.

UPDATE: After some extensive testing I can confirm this problem to be solved. I haven't once run into trouble waking it up from sleep. However, I occasionally get BSODs instead but this is most likely due to the SSDs and the drivers and not related to this problem.